Kauri Forestry in New Zealand a Protagonists' View I
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KAURI FORESTRY IN NEW ZEALAND A PROTAGONISTS' VIEW I. L. BARTON*and G. P. HORGAN? ABSTRACT Over the next decade the virtual cessation of timber extr~~ction from virgin kauri forests is inevitable. If Ne1,v Zealanders wish to use kauri timber in the future it will have to be taken from in- tensively managed regenerating stands designated for timber pro- duction, and from artificially established stands, probably in mix- tures with suitable exotics, which will act as nurse crops and per- haps yield an intermediate crop. This paper explores the various ways in which this might be done, reports on some recent and current experimental work i!! this field, and discusses a possible economic approach to kauri management. INTRODUCTION When considering management possibilities for kauri, two major problems become obvious. First, there are the technical aspects associated with growing the trees. Secondly, there is the economic viability of the operation. It has long been recognised that the management of New Zea- land indigenous trees was more difficult than that of exotic species, and that indigenous forest management could not satisfy New Zealand's demand for wood. Thus most state and private forest research has been directed toward exotics, particularly Pinus radiata. Radiata's early promise has been fulfilled many times over and today our pine plantations can produce all of our cellulose requirements, leaving a surplus to earn vital foreign exchange. This country will never be short of wood, but when the quality of the wood is considered new problems emerge. Man does not live by bread alone but requires a variable diet for com- plete health. So, too, with timber. Despite its great versatility, radiata pine cannot provide all of our wood needs. A finely built sideboard, made of pine and stained a mahogany colour, is a bit like making coffee out of acorns! *Hunua, Papakura, R.D. 3, Auckland. tForest Research Institute, Private Bag, Rotorua. 199 200 N.Z. IOURNAL OF FORESTRY It is strongly submitted that there is a place in our timber scene, and our economy, for timbers other than radiata pine, filling a place which pine cannot fill. These are special-use woods: the decorative timbers, the timbers with great strength, flexibility and durability. Kauri timber is well suited to many of these roles, especially boat building, turnery and veneer production. GROWING NATIVE TREES Because foresters did not understand the ecological require- ments of the various native species, early attempts to grow them were not very successful. The plantation systems applied to European and North American conifers did not seem to work with New Zealand trees. The cost and the many difficulties in- volved meant that those few attempts at indigenous management which were made did not usually continue for long enough for real benefit to accrue. The situation has now changed radically as shortages of quality timbers, both locally grown and imported, have become more apparent. The position of kauri in the market has now been con- siderably strengthened by the much higher and more realistic stumpages being paid for what is generally recognised as one of the world's finest softwoods. However, kauri is not only a timber of high intrinsic worth but also a tree capable of mannge- ment in several different ways. ESTABLISHMENT PHASE While kauri will regenerate on a wide variety of sites, a good seed source is vital. Where regeneration is inadequate the stock- ing can be supplemented by planting, since seed is easy to collect and nursery production relatively straightforward (Dakin and McClure, 1975; Lloyd, l978a). Most difficulties occur in the field immediately following plant- ing - or seed germination, if natural regeneration is being relied upon. Kauri is shade tolerant and, where natural forest processes prevail, seedlings usually sit beneath the canopy for 50 or 60 years (Lloyd. 1960). They grow extremely slowly and when light levels are high enough - usually following the breakdown of the nurse canopy - commence rapid growth. The most useful breakthrough in the whole area of indigenous management will be to reduce this establishment stage from 50 to KAURI FORESTRY 201 10 years. This can be done by keeping the seedlings growing at a rapid rate from the time of planting or germination. To achieve this seedlings must have an adequate supply of nutrients, mois- ture and light, and for severaI years weed competition must be controlled. At Hunua, in the Auckland Regional Authority's water catch- ment forests, south-east of Auckland, a wide variety of pilot ex- periments are being conducted, designed to find out as much as possible about the growth of kauri seedlings. Although much more work remains to be done, a standard procedure (given below) is followed when kauri is being planted into scrub-covered or forest sites, where natural regeneration is inadequate. Seedlings between 40 and 70 cm tall are planted in the autumn, as soon as the ground is moist enough. Tentative results show that seedlings will benefit from having the planting holes dug some months before and, if the pH is below 5, lime should be added. If the site has not had kauri growing on it before, the addition of leaf mould, containing mycorrhiza, will be beneficial. Trees are planted in groups of three, along a marked grid line and if necessary some of the shading plants are cut, so that over- head light is between 20 and 50% of full light. Plants are mulched with any available natural material. In spring the plants are fertilised with a long-lasting NPIC fertiliser. It is p3ssible that the addition of molybdenum may be beneficial. After the first year the seedlings are released from scrub competition which can be done by hand, or with chemicals which have a longer lasting effect. This releasing may be necessary again after three years. Final treatment comes at about age 5 when most of the scrub shading the seedlings is cut down to let in 60 to 90% of full light. Provided seedlings are well established by this stage they should continue to grow into small poles with no further treat- ment. This method, slightly modified, could also be used if it is wished to establish kauri seedlings under a nurse provided by an exotic plantation species - e.g., Pinus elliotti or Acacia nzelano- xylon. Once seedlings are established and growing at a reasonable rate, only one further releasing should be necessary - probably at about age 20. The most important factor is that the head of the tree must be kept in full light. 202 N.Z. JOURNAL OF FORESTRY MANAGEMENT OF POLE STANDS Results from silvicultural treatment of kauri pole stands indi- cate a favourable response to both thinning and the application of fertiliser. It seems that a stocking of about 700 stems per hectare of pole sized trees (5 to 30 cm d.b.h.) is close to optimum; application of a nitrogenous fertiliser has been shown to boost growth following thinning even further. Table 1 indicates the responses obtained from some of the treatments in an experiment at Hunua. These must be interpreted with care as it is almost impossible to find large enough areas of growth in order to properly replicate plot layouts. The Hunua plots were duplicated but variations in stocking, tree size, slope and soil type are too great to permit plot comparison. Instead, trees were randomly selected from each diameter class in the TABLE 1: GROWTH RATES OF POLE KAURI -- - Sfand Description and Location Treatment Natural regeneration at Mangatangi-Unthinned control 2174 stems/ha southern Hunua Thinned to: 1235 stems/ha Range 740 stems/ha 250 stems/ha Dominant poles Thinned to 740 stems/ha +Nitrogen (20-25 cm dia. class) +Phosphate (in 1967) +N and P. Unthinned control 2174 stems/ha Small poles Thinned to: m 1235 stms/ha (0-5 cm dia. class) 740 stems/ha (in 1967) 250 stems/ha Thinned to 740 stems/ha + Nitrogen f Phosphate +N and P. Plantation trees: plots established 1973 Cornwall Park, Auckland Planted 1926 346 stemslha Kirk's Bush, Papakura Planted 1955 566 stems/ha Scattered farm trees, Redshaw'sNaturally regenerating trees farm, Paparimu which were retained in 1965 when scrub was cleared and the area grassed. Annual application of molybdic superphosphate. Lime every three years. KAURI FORESTRY 293 control plots and compared with trees as close to the same size as possible in the other plots. Future work may have to rely on a comparison of tree, rather than plot response, unless very even areas of pole regrowth can be found. Despite these problems, the evidence presented indicates that silvicultural treatment considerably enhances the growth rate of kauri. Treatment has improved the growth rate of dominant trees (20 to 25 cm diameter class) by increasing periodic diameter increment between 170 and 290%. If the growth rates of the smallest trees in the stand (0 to 5 cm d.b.h.) are considered, the results are even more striking, with periodic diameter increments increasing 240 to 630%. Intermediate size classes exhibit similar patterns which fall between the two extremes. This response is particularly heartening, indicating that, while the larger trees will grow faster, the smaller trees show an even better response. Thus there are prospects for the perpetuation of an all-aged stand with regular selection logging of dominant trees. Diameter Breast Height (cm) Tree Volume - Total Stem (m3) 1%7 1978 c.a.i.* %c.a.i. 1467- 1978 c.a.i. % c.a.i. 21.3 25.2 0.355 1.7 0.251 0.373 0.0111 4.4 24.6 31.3 0.609 2.5 0.345 0.585 0.0218 6.3 20.7 30.1 0.855 4.1 0.193 0.471 0.0253 13.1 24.4 31.9 0.682 2.8 0.271 0.605 0.0304 11.2 20.7 32.0 1.027 5.0 0.196 0.605 0.0372 19.0 22.9 30.3 0.673 2.9 0.267 0.500 0.0212 7.9 25.0 34.3 0.845 2.5 0.321 0.735 0.0376 11.7 4.6 5.55 0.086 1.9 4.3 7.3 0.273 6.3 4.3 7.5 0.291 6.8 No trees in these plots in this size class 4.4 9.2 0.436 9.9 4.3 6.6 0.209 4.9 4.9 10.9 0.545 11.9 1973 1977 1973 1977 * c.a.i.